sleepycharlie :
I know this thread has been out for a while but I also can't get a rx 480 to work. You ever find a solution? I have a sufficient PSU and no combination of BIOS, drivers or anything will seem to work.. to much draw for the PCI slots regardless of whether or not it "should" be compatible? Goes black where the windows login screen should be. GPU fans stop trying to do anything.
I have experienced black screens with a recently bought XFX RX480 GTR Black and it seems that it boils down to the basic PSU not rising up to the card's needs. TL DR version is insufficient AMPS.
I own a Seasonic MII 620W PSU, that has two 12V rails with 24A each. Seasonic is considered a good manufacturer and 620W should be enough for an RX 480 but it isn't. After I installed the card I immediately launched the heaven benchmark to see its potential, but after one second after starting the screen turned black and I had to hard reset. I tried a game, but it had the same result. I tried everything that I found on the internet (DDU, "x" amount of drivers, BIOS updates, reinstalling windows, upgrading to win 10), nothing worked.
Then I decided to go at it "oldschool" and borrowed a more powerful (even though of lesser quality) High Power PSU with 700W and and a single 12V rail with 52.5A and needless to say the GPU card performed flawlessly. SInce my Seasonic has 620W and 2 rails with 24A (2x24A=48A???) it might not have been enough or the PSU has some kind of protection when the Amps that the card requires spyke.
I have come to this conclusion while observing the volts and amps listed in hwinfo64 for the gpu while the heaven benchmark was running. The watts usage never went above 130W but the Amps were all over the place with an average of 50A and spykes as high 120A (maybe this is where the PSU protection kicked in and shut off the power and the screen went black). I know it sounds unreasonably high for an amperage measurement but giving the the power issues that the RX 480 had at launch they are plausible.
My suggestion is to buy a good PSU with at least 700W and 52.5A on a single rail! I hope this helps somebody (to not waste 3 weeks troubleshooting RX480 gpu problems like I did)